Wireless communication apparatus and wireless communication method

ABSTRACT

There is provided a wireless communication apparatus and wireless communication method, which can perform information transfer, while suppressing interference to other terminal stations, and preventing a reduction of a transmission opportunity of other terminal stations. By causing the transmission power to be reduced, at the time when a traffic amount to be transmitted and received by itself increases, a terminal station which performs wireless access based on CSMA on a mesh network can suppress interference to other surrounding terminal stations, and can prevent a reduction of a transmission opportunity of other terminal stations. By measuring the number of and sizes of packets to be transmitted and received, it is possible for a terminal station to comprehend the traffic amount to be transmitted and received by itself, and perform a control of the transmission power by this.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/192,348, filed Nov. 15, 2018, which is acontinuation application of U.S. patent application Ser. No. 14/907,814,filed Jan. 26, 2016, now U.S. Pat. No. 10,154,464, which is a NationalStage Entry of PCT/JP2014/064470, filed May 30, 2014, which claims thebenefit of priority from Japanese Priority Patent Application JP2013-156361 filed in the Japan Patent Office on Jul. 29, 2013 which arehereby incorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

The technology disclosed in the present disclosure is related to awireless communication apparatus and wireless communication method whichmainly controls access to a media in accordance with an occupancy stateof the media, and for example, is related to a wireless communicationapparatus and wireless communication method which performs informationtransfer under a communication environment in which a plurality ofterminal stations are present by a same channel such as a mesh network.

BACKGROUND ART

In networks using wireless technology, a configuration method is widelyknown in which each terminal performs information transfer by asubordinate of a control station called an “access point” or the like.Each terminal station performs wireless communication, whilesynchronizing via the access point. For example, a terminal stationreserves a necessary band for information transfer, and uses a channelso that a collision with information transfer of other terminal stationsis not produced. However, in such a configuration method of a network,it may be necessary to perform wireless communication via the accesspoint, even at the time when performing asynchronous communication amongterminals, and there will be the problem of the utilization efficiencyof the channel being reduced by half.

In contrast to this, “Ad-hoc communication”, in which terminal stationsperform direct and asynchronous wireless communication not via an accesspoint, has been devised as another configuration method of a wirelessnetwork. For example, in an IEEE802.11 type wireless Local Area Network(LAN) system, in addition to an infrastructure mode in which an accesspoint intervenes, an Ad-hoc mode is prepared in which each terminalstation is operated by Peer-to-Peer with autonomous distribution,without distributing an access point.

In an Ad-hoc network, there is no means for synchronizing betweenterminal stations, such as an access point. Accordingly, it may benecessary to avoid competition, at the time where a plurality ofterminal stations use a same channel. Carrier Sense Multiple Access(CSMA) is known as a representative access system which avoidscompetition. In CSMA, a terminal station with transmission informationavoids collisions by a procedure, which confirms an occupancy state of amedia before transmission, and starts transmission in the case where themedia is clear.

Further, in CSMA, there is the problem of hidden terminals. Here, ahidden terminal is a terminal station in a state where mutual wirelesssignals do not arrive. Since a carrier of a hidden terminal is not ableto be detected, a collision with a hidden terminal is not able to beavoided by only CSMA.

RTS/CTS has been devised as a method which avoids collisions with hiddenterminals. A communication station of a transmission source transmits atransmission request packet Request To Send (RTS), and starts datatransmission by replying to a confirmation notification packet Clear ToSend (CTS) received from a communication station of a data transmissiondestination. Also, since a hidden terminal can receive at least one of aRTS and a CTS, a collision is avoided, by setting a transmission stopperiod of the station itself only for the period in which it is assumedthat data transfer is performed based on RTS/CTS.

However, in an access system based on CSMA, there will be the problem ofa transmittable opportunity being reduced in accordance with the numberof terminal stations attempting to perform information transmission on asame channel, even if a collision such as described above can beavoided. In the case where a certain terminal station does not want toperform communication with a terminal station, where a path loss withthis terminal present at an extremely adjacent location is remarkablysmall compared to a path loss with other stations, transmission forcollision avoidance will not be permitted, when receiving a signal ofanother terminal station (for example, refer to Patent Literature 1).That is, when a traffic amount increases on a channel, the interferenceamount to an adjacent terminal station will increase, and the band usedby the adjacent terminal station will be limited.

SUMMARY OF INVENTION Technical Problem

The inventors of the technology disclosed in the present disclosure haveprovided an excellent wireless communication apparatus and wirelesscommunication method, which can suitably perform information transfer,by a system which controls access to a media in accordance with anoccupancy state of the media.

The inventors of the technology disclosed in the present disclosure haveprovided an excellent wireless communication apparatus and wirelesscommunication method, which can suitably perform information transfer,while suppressing interference to other terminal stations, andpreventing a reduction of a transmission opportunity of other terminalstations.

Solution to Problem

The present application has been made in view of the aforementionedproblems. According to a technology described in claim 1, there isprovided a wireless communication apparatus including: a transmissionunit which transmits a wireless signal; a reception unit which receivesa wireless signal; an influence degree estimation unit which estimatesan influence degree given to a surrounding terminal station bytransmission data from the transmission unit; and a transmission powercontrol unit which controls a transmission power of the transmissionunit based on the influence degree.

According to a technology described in claim 2, the transmission powercontrol unit may control a transmission power of the transmission unitbased on the influence degree and a minimum transmission power capableof retaining a present data transfer.

According to a technology described in claim 3, a minimum transmissionpower capable of retaining a present data transfer may be calculatedbased on a data transfer speed necessary for presently transferred data,path loss information obtained from an RSSI or MCS, and a QoS of data.

According to a technology described in claim 4, at a time when theinfluence degree exceeds a prescribed value, the transmission powercontrol unit may change a transmission power of the transmission unit tothe minimum transmission power. According to a technology described inclaim 5, the transmission power control unit may change a transmissionpower to a transmission power corresponding to a relationship betweenthe influence degree and the minimum transmission power.

According to a technology described in claim 6, a signal detectioncapability in the reception unit may be controlled in accordance with achange in a transmission power of the transmission unit.

According to a technology described in claim 7, the wirelesscommunication apparatus may perform a communication operation by a meshnetwork, and a metric of a path may be recalculated in accordance with achange in a transmission power of the transmission unit.

According to a technology described in claim 8, the influence degreeestimation unit may measure a traffic amount to be handled by thetransmission unit and the reception unit as the influence degree.According to a technology described in claim 9, the influence degreeestimation unit may measure a traffic amount by counting the number ofpackets or a size of packet to be transmitted and received by thetransmission unit and the reception unit.

According to a technology described in claim 10, the influence degreeestimation unit may measure the number of links as the influence degree.

According to a technology described in claim 11, the influence degreeestimation unit may additionally estimate an influence degree given tothe wireless communication apparatus itself by transmission data fromthe transmission unit, and the transmission power control unit maycontrol a transmission power of the transmission unit based on theinfluence degree.

According to a technology described in claim 12, the influence degreeestimation unit may estimate a stability degree of a path of thewireless communication apparatus, and the transmission power controlunit may control a transmission power of the transmission unit based onthe stability degree of the path.

According to a technology described in claim 13, the influence degreeestimation unit may estimate the stability degree of the path based on avariation amount of a path metric, the number of links, and a trafficamount, in at least one fixed time in the past.

According to a technology described in claim 14, the influence degreeestimation unit may estimate whether or not there is a condition wherean addition of a new link is to be limited by the wireless communicationapparatus, and the transmission power control unit may control atransmission power in accordance with the condition. According to atechnology described in claim 15, the influence degree estimation unitmay estimate whether or not there is a condition where an addition of anew link is to be limited based on at least one of a present traffic andpower supply state.

According to a technology described in claim 16, the influence degreeestimation unit may estimate a link condition of a peer with a certainterminal station, and the transmission power control unit may control atransmission power in accordance with the link condition.

According to a technology described in claim 17, the influence degreeestimation unit may estimate the link condition based on at least one ofan MCS used for transmission to the terminal station, a reception RSSIfrom the terminal station, and a report value of an RSSI from theterminal station.

According to a technology described in claim 18, another terminalstation may be notified of information of a transmission power changedby the transmission power control unit.

According to a technology described in claim 19, a path loss may be backcalculated from an MCS used for a data packet transmitted from aterminal station of a communication partner, and a packet error rate ofa packet transmitted from the terminal station, and a transmission powerof the communication partner is estimated based on the path loss and areception RSSI.

According to a technology described in claim 20, there is provided awireless communication method including: an influence degree estimationstep which estimates an influence degree given to a surrounding terminalstation by transmission data; and a transmission power control stepwhich controls a transmission power at a time of data transmission basedon the influence degree.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the technology disclosed in the present disclosure, thereis provided an excellent wireless communication apparatus and wirelesscommunication method, which can suitably perform information transfer,while suppressing interference to other terminal stations, andpreventing a reduction of a transmission opportunity of other terminalstations.

In addition, the effects described in the present specification aremerely illustrative and demonstrative, and not limitative. In otherwords, the technology according to the present disclosure can exhibitother effects that are evident to those skilled in the art along with orinstead of the effects based on the present specification.

The object, features, and advantages of the present disclosure will bemade clear later by a more detailed explanation that is based on theembodiments of the present disclosure and the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a figure which shows a configuration of a wirelesscommunication apparatus 100 applying the technology disclosed in thepresent disclosure.

FIG. 2 is a figure which schematically shows a state in which aplurality of terminal stations are performing data transfer on a samechannel by using a wireless network (however, with no transmission powercontrol).

FIG. 3 is a figure which schematically shows an example of a usagecondition of the channel in the network environment shown in FIG. 2.

FIG. 4 is a figure which schematically shows a state in which aplurality of terminal stations are performing data transfer on a samechannel by using a wireless network (however, with transmission powercontrol).

FIG. 5 is a figure which schematically shows an example of a usagecondition of the channel in the network environment shown in FIG. 4.

FIG. 6 is a flow chart which shows a process procedure for the wirelesscommunication apparatus 100 to control a transmission power inaccordance with a traffic amount of itself.

FIG. 7 is a flow chart which shows another process procedure for thewireless communication apparatus 100 to control a transmission power inaccordance with a traffic amount of itself.

FIG. 8 is a figure which shows a graph representing a relationshipbetween a transmission power and a traffic amount.

FIG. 9 is a figure which illustrates a wireless network environment inwhich a transmittable range becomes non-uniform for each terminalstation.

FIG. 10 is a figure which shows a virtual transmittable range of anotherterminal station for a terminal station which has a threshold of signaldetection raised.

FIG. 11 is a flow chart which shows a process procedure for the wirelesscommunication apparatus 100 to control a transmission power inaccordance with the number of presently handled links.

FIG. 12 is a flow chart which shows another process procedure for thewireless communication apparatus 100 to control a transmission power inaccordance with the number of presently handled links.

FIG. 13 is a figure which shows a graph representing a relationshipbetween a transmission power and the number of links.

FIG. 14 is a flow chart which shows a process procedure for the wirelesscommunication apparatus 100 to control a transmission power inaccordance with a stability degree of a path.

FIG. 15 is a flow chart which shows another process procedure for thewireless communication apparatus 100 to control a transmission power inaccordance with a stability degree of a path.

FIG. 16 is a figure which shows a graph representing a relationshipbetween a transmission power and a variation amount (a stability degreeof a path).

FIG. 17 is a flow chart which shows a process procedure for the wirelesscommunication apparatus 100 to control a transmission power inaccordance with the condition of itself.

FIG. 18 is a flow chart which shows a process procedure for the wirelesscommunication apparatus 100 to positively control a transmission power.

FIG. 19 is a flow chart which shows a process procedure for estimating atransmission power without a notification of the transmission power.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the technology disclosed in the presentdisclosure will be described in detail while referring to the figures.

The technology disclosed in the present disclosure can be applied to awireless network to which an access system is applied based on CSMA,adopted by IEEE802.11 or the like. For example, the technology disclosedin the present disclosure can be applied to a mesh network such asprescribed by IEEE802.11s. In this type of wireless network, it isassumed that a plurality terminal stations are adjacently present whichuse a same channel. In such a case, problems such as shown in thefollowing (1) to (4) will be a concern.

Problem (1) Reduction of a Transmission Opportunity in the Case where aTraffic Amount Increases

-   In an access system based on CSMA, when a traffic amount increases    on a same channel, a transmittable opportunity reduces. In the case    where a certain terminal station does not want to perform    communication with a terminal station, where a path loss with this    terminal present at an extremely adjacent location is remarkably    small compared to a path loss with other stations, transmission for    collision avoidance will not be permitted, when receiving a signal    of another terminal station. That is, when a traffic amount    increases on a channel, the interference amount to an adjacent    terminal station will increase, and the band used by the adjacent    terminal station will be limited.

Problem (2) Enlargement of Unnecessary Interference

-   In an access system based on CSMA, when a certain terminal station    performs transmission and reception, this data becomes interference    for adjacent terminal stations other than the reception station    which use a same channel. When performing data transmission with a    transmission power higher than necessary, by a link with a good    transfer environment, a transmission opportunity of other terminal    stations becomes wastefully reduced.

Problem (3) Occurrence of a Relay Opportunity by a Terminal Station witha Low Power Supply Capacity

-   In a mesh network such as prescribed by IEEE802.11s, a mutual    connection is performed, between transmission and reception terminal    stations at which electric waves do not directly reach, by multi-hop    communication in which an adjacent terminal station performs a    relay. In the case where a plurality of paths exist, a metric is    calculated for each path, and the path having the best metric is    selected. A metric is a value which shows the closeness of a path,    and information is generally used which shows the quality of a link,    such as the number of hops or transfer delay, a strength of a    wireless link, a bandwidth, or a channel occupation time (for    example, refer to Patent Literature 2). However, path selection is    hardly ever performed in consideration of the circumstances of a    relaying terminal station.

There are terminal stations in which stable power is supplied from an ACpower supply, and there are terminal stations which operate bybatteries. When performing a relay of another terminal station, in astate where a power supply capacity is low, it can become difficult forthe latter to secure a necessary power supply for data transfer ofitself. Further, cases are possible where a terminal station, whichperforms a large amount of data transfer with only an adjacent terminalstation, is temporarily not able to perform a relay. The circumstancesfor each of such terminal stations is not considered, in path selectionbased on a metric calculation. It can also be considered that a terminalstation, for which a relay is not wanted to be performed, is cut fromthe mesh network, and a separate link is set by Wi-Fi Direct or thelike. However, in the case where the wireless band is tight, such ashaving a large number of terminal stations adjacently present which usea same channel, such a separate link will become interference of theadjacent terminal stations, and so a fundamental solution is notreached.

Problem (4) Difficulty of an Estimation of a Path Loss in the Case wherePerforming Transmission Power Control

-   A terminal station measures a reception power (RSSI: Received Signal    Strength Indication) of a packet received by a terminal station of a    communication partner, and estimates a path loss by taking a    difference of transmission powers. Also, an appropriate Modulation    and Coding Scheme (MCS) of a packet to be transmitted to this    communication partner is determined, based on information of this    path loss and a packet loss rate (an MCS is an index number which    shows a combination of a Phy rate, an encoding rate, and a    modulation system used for packet transmission). However, the above    described estimation method of a path loss will have a precondition    of the transmission power of a terminal station which becomes a    communication partner being fixed (or already known). In the case    where each terminal station performs transmission power control, the    transmission power is not fixed, and so a path loss is not able to    be estimated by measuring an RSSI. Therefore, a terminal station is    not able to select an appropriate MCS, and efficient use of a    channel becomes difficult.

Accordingly, in the technology disclosed in the present disclosure, in awireless network to which an access system is applied based on CSMA, atleast one part of a terminal station suppresses interference to otherterminal stations, and causes a transmission opportunity of otherterminal stations to not be wastefully reduced, by controlling thetransmission power based on an influence degree given to surroundingterminal stations by data transmission of the station itself.

FIG. 1 shows a configuration of a wireless communication apparatus 100,applying the technology disclosed in the present disclosure, which canoperate as a terminal station in a wireless network to which an accesssystem is applied based on CSMA. The substance of the wirelesscommunication apparatus 100 is one of various types of informationdevices in which a wireless LAN function is installed, such as amultifunctional information terminal such as a personal computer or asmartphone, a network printer, or a network drive, in addition to awireless device,.

The illustrated wireless communication apparatus 100 includes atransmission unit 110, a reception unit 120, a transmission andreception antenna 101 shared by the transmission unit 110 and thereception unit 120, and an upper layer processing unit 130 whichperforms the processes of transmission data to be transmitted from thetransmission unit 110 and reception data received by reception unit 120.The transmission unit 110 and the reception unit 120 mainly performprocesses of a physical (Phy) layer. Further, the upper layer processingunit 130 performs processes of a media connection control (Media AccessControl: MAC) based on CSMA, and processes corresponding to an upperlayer more than that of a MAC layer.

The upper layer processing unit 130 starts a prescribed application, forexample, in accordance with a request of a user or the like. Theapplication generates transmission data to be transmitted to a terminalstation which becomes a communication partner, and performs a process ofreception data which can be sent from the communication partner.

The transmission unit 110 includes a channel encoding unit 111, amodulation unit 112, an RF transmission unit 113, and a transmissionpower control unit 114.

The channel encoding unit 111 encodes the transmission data handed overfrom the upper layer processing unit 130, and additionally performserror correction encoding. The modulation unit 112 applies a modulationprocess such as OFDM to the error correction encoded transmission data.Also, the RF transmission unit 113 converts a digital signal after beingmodulated into an analogue signal, additionally performs an RFtransmission process such as up-conversion or power amplification to anRF band, and afterwards performs sending from the antenna 101. Thetransmission power control unit 114 outputs an instruction value ofpower amplification to the RF transmission unit 113, in accordance withan instruction from an influence degree estimation unit 124, which willbe described below, and controls the transmission power.

The reception unit 120 includes an RF reception unit 121, a demodulationunit 122, a channel decoding unit 123, an influence degree estimationunit 124, and a signal detection capability control unit 125.

The RF reception unit 121 performs an RF reception process such as lownoise amplification, down-conversion, or conversion to a digital signal,of a signal received by the antenna 101. The demodulation unit 122applies a demodulation process such as OFDM to a received digitalsignal. Also, the channel decoding unit 123 decodes reception data afterbeing demodulated, and hands it over to the upper layer processing unit130, by additionally performing error correction.

The signal detection capability control unit 125 changes a signaldetection capability in the demodulation unit 122 within the receptionunit 120, for example, in accordance with an instruction from theinfluence degree estimation unit 124. Here, signal detection generallydetects the presence of signal with a preamble portion of a receivedpacket, and is attached to a position as a part of a synchronizationprocess. Therefore, the signal detection capability control unit 125 cancontrol the signal detection capability by changing a threshold set forpreamble detection. Alternatively, in the case where a switch andattenuator are inserted into a signal reception system and the signaldetection capability is wanted to be lowered, a means can be taken foradopting a reception signal as a reception signal via an attenuator.Alternatively, a means can be taken for adjusting a bit width of ADconversion. In the case where the signal detection capability islowered, a large quantitative error is allowed by performing ADconversion with a small bit width, and an SNR of a received signal iscaused to be equivalently reduced.

The influence degree estimation unit 124 extracts a characteristicamount from transmission data to be input to the channel encoding unit111 and reception data after being decoded by the channel decoding unit123, and estimates an influence degree given to surrounding terminalstations at the time when performing data transmission by the presenttransmission power from the transmission unit 110, based on thisextraction result. A traffic amount to be transmitted and received byitself, the number of links, a metric of a path, a stability of a pathor the like is extracted, for example, as the characteristic amount. Inorder for the influence degree estimation unit 124 to extract a trafficamount, the number of packets or a size of packet to be transmitted andreceived by itself is counted, by monitoring the channel encoding unit111 and the channel decoding unit 123.

Also, the influence degree estimation unit 124 suppresses interferenceto other terminal stations, and arbitrarily outputs a change instructionof the transmission power to the transmission power control unit 114, soas not to cause a transmission opportunity of other terminal stations tobe reduced. Further, the influence degree estimation unit 124 instructsa change of the signal detection capability in the demodulation unit 122to the signal detection capability control unit 125, so that atransmittable range from the transmission unit 11 and a receivable rangein the reception unit 120 are balanced, in accordance with a change ofthe transmission power. The details of a control of the transmissionpower and the signal detection capability will be made in the belowdescription.

Further, in addition to an influence degree given to surroundingterminal stations, the influence degree estimation unit 124 can estimatea communication condition of itself, based on the above describedextracted characteristic amount or a measurement value other than this.The stability degree of a communication partner and this path, the roomto accept new traffic, the room of a link condition of a peer or thelike can be included, for example, as the communication condition of theterminal station itself. The details will refer to the third embodiment,which will be described below.

Note that, the influence degree estimation unit 124 can be arranged, notonly in the reception unit 120, but also in a separate location, such asthe transmission unit 110 or the upper layer processing unit 130.

Embodiment 1

-   Here, an embodiment will be described in which a terminal station    controls the transmission power in accordance with a traffic amount,    in a wireless network in which access control is performed to a    media in accordance with an occupancy state of the media.

FIG. 2 schematically shows a state in which a plurality of terminalstations are performing data transfer on a same channel by using awireless network. However, in the same figure, each of the terminalstations are not performing a control of the transmission power.

In the illustrated example, 6 terminal stations from STA0 up to STA5 arepresent. Also, data transmission is performed from the STA0 to the STA1,in the direction shown by arrow 201, data transmission is performed fromthe STA2 to the STA3, in the direction shown by arrow 202, and datatransmission is performed from the STA4 to the STA5, in the directionshown by arrow 203. Note that, here, it is assumed to be the case whereeach terminal station is connected by peer-to-peer and performstransfer, such as Wi-Fi Direct or a mesh network. Further, thetransmittable range of the STA0 in the case where not controlling thetransmission power is represented by the oval shown by reference numeral204. While the STA1, 2, 3, and 4 are within the transmittable range 204of the STA0, the STA5 is outside of this.

Further, FIG. 3 schematically shows an example of a usage condition ofthe channel in the network environment shown in FIG. 2. Within thefigure, the horizontal axis is set to a time axis, and channeloccupation times 301 to 307 of each terminal station are shown by grayblocks.

The STA1, 2, 3, and 4 can receive a transmission signal from the STA0.Accordingly, it may be necessary for these terminal stations to stoptransmission of data, by detecting an occupancy state of a media, at thetime bands 301, 302, 303, and 304 in which the STA0 is performing datatransmission. Therefore, in the case where a traffic amount of the STA0is large, the STA1, 2, 3, and 4 will have a reduced opportunity of datatransmission.

In a media access control system by CSMA, a transmission opportunity isallocated equally to all of the terminal stations including the STA0.However, in the case where a traffic amount of the STA0 obtaining atransmission opportunity is large, there will be a reduction of atransmission opportunity of the terminal stations other than this.

On the other hand, FIG. 4 schematically shows a state in which aplurality of terminal stations are performing data transfer on a samechannel by using a wireless network, in the case where transmissionpower control is performed.

In the example shown in FIG. 4, data transmission is performed from theSTA0 to the STA1, in the direction shown by arrow 401, data transmissionis performed from the STA2 to the STA3, in the direction shown by arrow402, and data transmission is performed from the STA4 to the STA5, inthe direction shown by arrow 403.

Here, when an increase of a traffic amount to be transferred by itselfis perceived, the STA0 examines a change of the transmission power.Specifically, the STA0 calculates a minimum transmission power whichbecomes a necessary minimum limit at which data transmission is capable,by taking into consideration a path loss with the STA1 which is acommunication partner, a necessary data transfer speed, and a Quality ofService (QoS). Then, the STA0 performs data transfer to the STA1, byusing the obtained transmission power. In this way, as shown in FIG. 4,the transmittable range of the STA0 narrows such as shown by thereference numeral 404, and the STA3 and the STA4 are outside from thisrange.

At this time, by also adjusting the transmittable range of the STA3 andthe STA4, the STA3 and the STA4 can occupancy the channel, regardless ofthe presence or not of data transmission of the STA0, when it is assumedthat an electric wave does not reach to the STA0.

FIG. 5 schematically shows an example of a usage condition of thechannel in the network environment shown in FIG. 4. Within the figure,the horizontal axis is set to a time axis, and channel occupation times501 to 512 of each terminal station are shown by gray blocks. Asillustrated, it is possible to perform data transfer by using a samechannel, in the time bands 508, 509, 510, 511, and 512 which overlapwith the time bands 501, 502, 503, and 504 in which the STA0 isperforming data transmission. In this way, by having the STA0 controlthe transmission power, a reduction of a transmission opportunity ofsurrounding terminal stations can be prevented.

Note that, while an illustration is omitted, in the case where a trafficamount to be handled by itself is low, the STA0 considers that there isa low probability of causing a transmission opportunity of otherterminal stations to be reduced, and performs data transfer by settingto a usual transmission power.

FIG. 6 shows a process procedure, in the form of a flow chart, for thewireless communication apparatus 100, which operates as the STA0, tocontrol the transmission power in accordance with a traffic amount ofitself.

The influence degree estimation unit 124 counts the number of packets ora size of packet to be transmitted and received by itself, by monitoringthe channel encoding unit 111 and the channel decoding unit 123, andmeasures a traffic amount to be handled by this wireless communicationapparatus 100, as an influence degree given to surrounding terminalstations (step S601).

Then, the influence degree estimation unit 124 checks whether or not theobtained traffic amount exceeds a prescribed threshold (step S602).

Here, in the case where the traffic amount exceeds a prescribedthreshold (Yes in step S602), an instruction is output from theinfluence degree estimation unit 124 to the transmission power controlunit 114, so as to perform a change of the transmission power to be datatransmitted from the transmission unit 110.

In order for a change of the transmission power, first, a minimumtransmission power is calculated (step S603). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data.

Then, the transmission power control unit 114 outputs an instruction ofpower amplification to the RF transmission unit 113, so as to change tothe minimum transmission power (step S604). Note that, the calculatedtransmission power is used for all of the transmission packets includinga beacon.

By using a minimal transmission power corresponding to the service ofdata to be transferred or a QoS, the STA0 performing data transfer cansuppress interference to other terminal stations, and can prevent areduction of a transmission opportunity of other terminal stations.

On the other hand, in the case where the traffic amount does not exceeda prescribed threshold (No in step S602), it can be considered thatthere is a low possibility of causing a transmission opportunity ofsurrounding terminal stations to be reduced. Accordingly, the influencedegree estimation unit 124 performs an instruction to the transmissionpower control unit 114 so as to return, to the original state, thetransmission power reduced to the minimum transmission power (stepS607), and secures a transmittable range of the station itself.

At the time when the transmission power is changed in step S604 or stepS607, in combination with this, the signal detection capability controlunit 125 performs an adjustment so as to not detect a packet receivedwith a low power, by changing the signal detection capability in thedemodulation unit 122 within the reception unit 120 (step S605).However, it will be arbitrary whether or not an adjustment of the signaldetection capability is also performed, along with a change of thetransmission power.

Further, at the time when the transmission power is changed in step S604or step S607, there will be the possibility that discrepancies in theactual value are produced with the calculated path metric, and defectsoccur such as a packet loss of the transmission data. Accordingly, arecalculation of the path metric is executed (step S606). For example, arecalculation of the path metric is executed, by having the wirelesscommunication apparatus 100 transmit a path request (PREQ) at the timewhen operating as a transmission source of multi-hop transmission, ortransmit a path error (PERR) at the time when operating as a relaystation. By changing the transmission power, and afterwards performing arecalculation of the metric by the transmission of a PREQ or PERR, itbecomes possible for a terminal station to select a path correspondingto the transmission power at an early stage. However, it will bearbitrary whether or not a recalculation of the path metric is alsoperformed, along with a change of the transmission power.

Further, FIG. 7 shows another process procedure, in the form of a flowchart, for the wireless communication apparatus 100, which operates asthe STA0, to control the transmission power in accordance with a trafficamount of itself.

First, the influence degree estimation unit 124 counts the number ofpackets or a size of packet to be transmitted and received by itself, bymonitoring the channel encoding unit 111 and the channel decoding unit123, and measures a traffic amount to be handled by this wirelesscommunication apparatus 100, as an influence degree given to surroundingterminal stations (step S601).

Next, in order for a change of the transmission power, first, a minimumtransmission power is calculated (step S702). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data (same asabove).

Then, when the transmission power is determined, based on a relationshipbetween the traffic amount obtained in step S701 and the minimumtransmission power obtained in step S702 (step S703), the transmissionpower determination unit 114 outputs an instruction of poweramplification to the RF transmission unit 113, so as to change to thistransmission power (step S704). Note that, the changed transmissionpower is used for all of the transmission packets including a beacon.

Next, the signal detection capability control unit 125 performs anadjustment so as to not detect a packet received with a low power, bychanging the signal detection capability in the demodulation unit 122within the reception unit 120 (step S705). However, it will be arbitrarywhether or not an adjustment of the signal detection capability is alsoperformed, along with a change of the transmission power.

Further, since discrepancies in the actual value are produced with thecalculated path metric, and defects occur such as a packet loss of thetransmission data, by the transmission power after being changed, arecalculation of the path metric is executed (step S706). However, itwill be arbitrary whether or not a recalculation of the path metric isalso performed, along with a change of the transmission power.

Here, a supplemental remark will be described for a method whichdetermines the transmission power based on a relationship between thetraffic amount and the minimum transmission power in step S703.

For example, a look-up-table which obtains a transmission power from thetraffic amount and the minimum transmission power can be created inadvance based on experiments, simulation calculations or the like, thiscan be stored in a Read Only Memory (ROM) or the like, and atransmission power can be obtained, by applying the values calculated insteps S701 and S702 to this look-up-table.

Alternatively, an appropriate transmission power can be obtained, bycreating a graph representing a relationship between the transmissionpower and the traffic amount, and applying the traffic amount obtainedin step S701 to this graph, such as shown in FIG. 8, based on the valuescalculated by steps S701 and S702. In the graph shown in FIG. 8, amaximum value 801 of the transmission power is a value, for example,which is determined by an output limit of the RF transmission unit 113within the transmission unit 110. Further, a minimum value 802 of thetransmission power is a transmission power which becomes a necessaryminimum limit at which the present data transfer is able to be retained,and is calculated in step S702. Further, a lower threshold 1 and anupper threshold 2 of the traffic amount shown by reference numerals 803and 804 are determined by a request or the like of an application whichrequests data transfer.

In this way, when the present traffic amount 806 obtained in step S701is applied to the obtained graph 805, a transmission power 807 isdetermined.

Further, a supplemental remark will be described for a control of thesignal detection capability of the reception unit 120, performed insteps S604 and S704.

When each of the terminal stations individually perform transmissionpower control such as described above, a condition will occur in whichthe transmission power is different according to the terminal stations.In such a case, there is a high possibility that the terminal stationwith the largest transmission power will obtain a transmissionopportunity, and there is a concern that a transmission opportunity willbecome non-uniform for each of the terminal stations.

FIG. 9 illustrates a wireless network environment in which atransmittable range becomes non-uniform for each of the terminalstations. In the illustrated example, 6 terminal stations from STA0 upto STA5 are present. Also, data transmission from the STA0 to the STA1is performed, in the direction shown by arrow 901, data transmissionfrom the STA2 to the STA3 is performed, in the direction shown by arrow902, and data transmission from the STA4 to the STA5 is performed, inthe direction shown by arrow 903. Note that, here, it is assumed to bethe case where each terminal station is connected by peer-to-peer andperforms transfer, such as Wi-Fi Direct or a mesh network.

The STA0 lowers the transmission power. The transmittable range of theSTA0 becomes small, such as represented by the oval shown by referencenumeral 904. On the other hand, the STA4 keeps a large transmissionpower. The transmittable range of the STA4 is represented by the ovalshown by reference numeral 905, and includes the STA0. When wirelessaccess is performed based on CSMA in such a condition, the STA0 candetect a signal transmitted from the STA4, and so can stop atransmission of data, for example, when receiving an RTS packet of theSTA4. On the other hand, the STA4 is not able to detect a signal of theSTA0, and so is capable of performing data transmission of itself, forexample, without detecting an RTS packet of the STA0.

Since such a non-uniformity of the transmission opportunity reduces, theSTA0 performs a control together with the signal detection capability ofitself, at the time when changing the transmission power. That is, inthe STA0, a threshold of signal detection changes in the demodulationunit 122 within the reception unit 120. The STA0 narrows the signaldetection range, by raising a threshold of signal detection in thedemodulation unit 122, at the time when reducing the transmission powerof itself.

FIG. 10 shows a virtual transmittable range of the STA4 for the STA0, atthe time when the STA0 raises a threshold of signal detection. Asillustrated, at the time when the STA0 reduces a transmittable range1001 of itself, an effect similar to narrowing the transmittable rangeof the STA4 such as shown by reference numeral 1002 can be obtained, byadditionally narrowing the signal detection range. Since the STA0 is notable to detect a signal of the STA4, it becomes possible to perform datatransmission of itself, for example, without detecting an RTS packet ofthe STA4.

Further, a supplemental remark will be described for a recalculation ofthe path metric, performed in steps S605 and S705.

In order to select a path, in a wireless mesh network includingIEEE802.11s, a value which shows the closeness of the path, that is, apath metric, is calculated. In IEEE802.11s, the time which a channel isoccupied at the time when transmitting a data frame, calculated from atransmission speed of a physical layer, a packet error rate or the like,is prescribed as a default path metric.

In a wireless network, it is assumed that the condition of thepropagation environment and each of the terminal stations changes momentby moment. Accordingly, a calculation of the path metric is performed atfixed time intervals. However, when a terminal station changes thetransmission power or the signal detection capability such as describedabove, there will be a high possibility that discrepancies in the actualvalue are produced with the calculated path metric, and defects occursuch as a packet loss of the transmission data. Therefore, in the casewhere changing the transmission power or the signal detection capabilityof itself, it is preferable for a terminal station to perform arecalculation of the path metric.

A recalculation of the path metric is executed by having a terminalstation of a transmission source transmit a path request PREQ packet,similar to at the time of a usual path signal. However, at the time whena terminal station, which is a relay node and not a transmission sourceof data, changes the transmission power, a path metric is not able to beobtained by a method which transmits a PREQ. Accordingly, a terminalstation, which is a relay node, transmits a path error PERR packet to aterminal station of a transmission source. PERR is originally used inthe case where a mesh path set for a deterioration of a wireless link orthe like is not able to be used, and prompts a refresh of the mesh path(a recalculation of the path metric) to a transmission source.Therefore, the path metric is recalculated according to this operation.

According to the first embodiment, by causing the transmission power tobe reduced, at the time when a traffic amount to be transmitted andreceived by itself increases, a terminal station which performs wirelessaccess based on CSMA on a mesh network can suppress interference toother surrounding terminal stations, and can prevent a reduction of atransmission opportunity of other terminal stations. That is, the abovedescribed problems (1) and (2) can be solved. By measuring the number ofand sizes of packets to be transmitted and received, it is possible fora terminal station to comprehend the traffic amount to be transmittedand received by itself, and perform a control of the transmission powerby this.

Further, according to the first embodiment, by using a minimaltransmission power corresponding to the service of data to betransferred or a QoS, a terminal station can suppress interference toother terminal stations, and can prevent a reduction of a transmissionopportunity of other terminal stations.

Further, according to the first embodiment, by performing a change of asignal detection capability together with a change in a transmissionpower of itself, a terminal station can reduce the non-uniformity of atransmission opportunity between terminal stations.

Further, according to the first embodiment, by changing a transmissionpower or a signal detection capability of itself, and afterwardsperforming a recalculation of a path metric by the transmission of aPREQ or PERR, it becomes possible for a terminal station to perform aselection of a path corresponding to the transmission power at an earlystage.

Embodiment 2

-   Here, an embodiment will be described in which a terminal station    controls the transmission power in accordance with the number of    links.

There is a high possibility that a terminal station with a large numberof current links will perform communication with many terminals. Thatis, it is suggested that there is a high number of terminal stationswhich receive an influence due to a channel occupation of a terminalstation with a large number of links. Therefore, it can be consideredthat, by reducing the transmission power of a terminal with a largenumber of links, a reduction of a transmission opportunity of otherterminal stations can be prevented. FIG. 11 shows a process procedure,in the form of a flow chart, for the wireless communication apparatus100 to control the transmission power in accordance with the number ofpresently handled links.

The influence degree estimation unit 124 measures a link numberpresently handled by this wireless communication apparatus 100, as aninfluence degree given to surrounding terminal stations (step S1101).

Then, the influence degree estimation unit 124 checks whether or not theobtained number of links exceeds a prescribed threshold (step S1102).Here, in the case where the number of links exceeds a prescribedthreshold (Yes in step S1102), an instruction is output from theinfluence degree estimation unit 124 to the transmission power controlunit 114, so as to perform a change of the transmission power to be datatransmitted from the transmission unit 110.

In order for a change of the transmission power, first, a minimumtransmission power is calculated (step S1103). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data.

Then, the transmission power control unit 114 outputs an instruction ofpower amplification to the RF transmission unit 113, so as to change tothe minimum transmission power (step S1104). Note that, the calculatedtransmission power is used for all of the transmission packets includinga beacon.

By causing the transmission power to be reduced in accordance with anincrease of the number of links to be handled, a terminal station cansuppress interference to other terminal stations, and can cause atransmission opportunity of other terminal stations to be improved.

On the other hand, in the case where the number of links currentlyhandled does not exceed a prescribed threshold (No in step S1102), itcan be considered that there is a low possibility of causing atransmission opportunity of surrounding terminal stations to be reduced.Accordingly, the influence degree estimation unit 124 performs aninstruction to the transmission power control unit 114 so as to return,to the original state, the transmission power reduced to the minimumtransmission power (step S1107), and secures a transmittable range ofthe station itself.

At the time when the transmission power is changed in step S1104 or stepS1107, in combination with this, the signal detection capability controlunit 125 performs an adjustment so as to not detect a packet receivedwith a low power, by changing the signal detection capability in thedemodulation unit 122 within the reception unit 120 (step S1105) (sameas above). However, it will be arbitrary whether or not an adjustment ofthe signal detection capability is also performed, along with a changeof the transmission power.

Further, at the time when the transmission power is changed in stepS1104 or step S1107, there will be the possibility that discrepancies inthe actual value are produced with the calculated path metric, anddefects occur such as a packet loss of the transmission data.Accordingly, a recalculation of the path metric is executed (stepS1106). For example, a recalculation of the path metric is executed, byhaving the wireless communication apparatus 100 transmit a path request(PREQ) at the time when operating as a transmission source of multi-hoptransmission, or transmit a path error (PERR) at the time when operatingas a relay station. By changing the transmission power, and afterwardsperforming a recalculation of the metric by the transmission of a PREQor PERR, it becomes possible for a terminal station to select a pathcorresponding to the transmission power at an early stage (same asabove). However, it will be arbitrary whether or not a recalculation ofthe path metric is also performed, along with a change of thetransmission power.

Further, FIG. 12 shows another process procedure, in the form of a flowchart, for the wireless communication apparatus 100 to control thetransmission power in accordance with the number of presently handledlinks.

First, the influence degree estimation unit 124 measures the number oflinks currently handled by this wireless communication apparatus 100, asan influence degree given to surrounding terminal stations (step S1201).

Next, in order for a change of the transmission power, first, a minimumtransmission power is calculated (step S1202). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data (same asabove).

Then, when the transmission power is determined, based on a relationshipbetween the number of links obtained in step S1201 and the minimumtransmission power obtained in step S1202 (step S1203), the transmissionpower determination unit 114 outputs an instruction of poweramplification to the RF transmission unit 113, so as to change to thistransmission power (step S1204). Note that, the changed transmissionpower is used for all of the transmission packets including a beacon.

Next, the signal detection capability control unit 125 performs anadjustment so as to not detect a packet received with a low power, bychanging the signal detection capability in the demodulation unit 122within the reception unit 120 (step S1205) (same as above). However, itwill be arbitrary whether or not an adjustment of the signal detectioncapability is also performed, along with a change of the transmissionpower.

Further, since discrepancies in the actual value are produced with thecalculated path metric, and defects occur such as a packet loss of thetransmission data, by the transmission power after being changed, arecalculation of the path metric is executed (step S1206). However, itwill be arbitrary whether or not a recalculation of the path metric isalso performed, along with a change of the transmission power.

Here, a supplemental remark will be described for a method whichdetermines the transmission power based on a relationship between thenumber of links and the minimum transmission power in step S1203.

-   For example, a look-up-table which obtains a transmission power from    the number of links and the minimum transmission power can be    created in advance based on experiments, simulation calculations or    the like, this can be stored in a Read Only Memory (ROM) or the    like, and a transmission power can be obtained, by applying the    values calculated in steps S1201 and S1202 to this look-up-table.

Alternatively, an appropriate transmission power can be obtained, bycreating a graph representing a relationship between the transmissionpower and the number of links, and applying the number of links obtainedin step S1201 to this graph, such as shown in FIG. 13, based on thevalues calculated by steps S1201 and S1202. In the graph shown in FIG.13, a maximum value 1301 of the transmission power is a value, forexample, which is determined by an output limit of the RF transmissionunit 113 within the transmission unit 110. Further, a minimum value 1302of the transmission power is a transmission power which becomes anecessary minimum limit at which the present data transfer is able to beretained, and is calculated in step S1202. Further, a lower threshold 1and an upper threshold 2 of the number of links shown by referencenumerals 1303 and 1304 are determined by a request or the like of anapplication which requests data transfer. In this way, when the presentnumber of links 1306 obtained in step S1301 is applied to the obtainedgraph 1305, a transmission power 1307 is determined.

According to the second embodiment, by causing the transmission power tobe reduced, at the time when the number of links handled by itselfincreases, a terminal station which performs wireless access based onCSMA on a mesh network can suppress interference to other surroundingterminal stations, and can prevent a reduction of a transmissionopportunity of other terminal stations. That is, the above describedproblems (1) and (2) can be solved.

Further, according to the second embodiment, by using a minimaltransmission power corresponding to the service of data to betransferred or a QoS, a terminal station can suppress interference toother terminal stations, and can prevent a reduction of a transmissionopportunity of other terminal stations.

Further, according to the second embodiment, by performing a change of asignal detection capability together with a change in a transmissionpower of itself, a terminal station can reduce the non-uniformity of atransmission opportunity between terminal stations.

Further, according to the second embodiment, by changing a transmissionpower or a signal detection capability of itself, and afterwardsperforming a recalculation of a path metric by the transmission of aPREQ or PERR, it becomes possible for a terminal station to perform aselection of a path corresponding to the transmission power at an earlystage.

Embodiment 3

-   In the first and second embodiments, a terminal station performs a    control of the transmission power, by taking into consideration an    influence degree given to other terminal stations by data    transmission and reception of itself. For example, an influence to    other terminal stations is estimated based on a traffic amount to be    transmitted and received by itself and the number of handled links,    and interference to other terminal stations is suppressed by    controlling the transmission power. In contrast to this, in a third    embodiment, a terminal station performs a control of the    transmission power, by taking into consideration an influence degree    given to itself by data transmission and reception of itself.

It is possible for a terminal station to control the transmission poweraccording to the condition of the terminal station itself, regardless ofthe condition of the surroundings, and an effect by this can also beobtained. Hereinafter, a number of methods will be described in detailin which the transmission power is controlled by the circumstances of aterminal station itself.

(1) Transmission Power Control at the Time when a Communication Partnerand this Path are Stable

At the time when a communication partner of traffic handled by aterminal station, and this path, are stable, it can be considered thatit will be difficult for sudden variations in a wireless link to occurin this terminal station. Therefore, by lowering the transmission powersecured as a margin for surely performing data transmission, theterminal station can cause a reduction of a transmission opportunity ofother terminal stations to be improved. For example, the stabilitydegree of a path can be estimated based on a variation amount of a pathmetric, the number of links, and a traffic amount. Accordingly, theinfluence degree estimation unit 124 estimates the stability degree of apath as an influence degree given to itself by data transmission andreception of itself, and the transmission power control unit 114performs a control of the transmission power in accordance with thestability degree of the path.

FIG. 14 shows a process procedure, in the form of a flow chart, for thewireless communication apparatus 100 to control the transmission powerin accordance with the stability degree of a path.

The influence degree estimation unit 124 measures at least one fromamong a path metric, the number of links, and a traffic amount only fora fixed time, and retains a variation amount of a past fixed time, as avalue which shows the stability degree of a path (step S1401).

Then, the influence degree estimation unit 124 checks whether or not theretained variation amount is at a prescribed threshold or below (stepS1402).

Here, in the case where the variation amount is at a prescribedthreshold or below (Yes in step S1402), the path of this terminalstation can be considered to be stable. Therefore, an instruction isoutput from the influence degree estimation unit 124 to the transmissionpower control unit 114, so as to perform a change of the transmissionpower which performs data transmission from the transmission unit 110.

In order for a change of the transmission power, first, a minimumtransmission power is calculated (step S1403). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data.

Then, the transmission power control unit 114 outputs an instruction ofpower amplification to the RF transmission unit 113, so as to change tothe minimum transmission power (step S1404). Note that, the calculatedtransmission power is used for all of the transmission packets includinga beacon.

By causing the transmission power to be reduced at the time when a pathis stable, a terminal station can suppress interference to otherterminal stations, and can cause a transmission opportunity of otherterminal stations to be improved.

On the other hand, in the case where the variation amount exceeds aprescribed threshold (No in step S1402), the path of this terminalstation can be considered to be not stable. In this case, it can beconsidered that it may be necessary to secure a margin of thetransmission power for surely performing data transmission. Accordingly,the influence degree estimation unit 124 performs an instruction to thetransmission power control unit 114 so as to return, to the originalstate, the transmission power reduced to the minimum transmission power(step S1407).

At the time when the transmission power is changed in step S1404 or stepS1407, in combination with this, the signal detection capability controlunit 125 performs an adjustment so as to not detect a packet receivedwith a low power, by changing the signal detection capability in thedemodulation unit 122 within the reception unit 120 (step S1405) (sameas above). However, it will be arbitrary whether or not an adjustment ofthe signal detection capability is also performed, along with a changeof the transmission power.

Further, at the time when the transmission power is changed in stepS1404 or step S1407, there will be the possibility that discrepancies inthe actual value are produced with the calculated path metric, anddefects occur such as a packet loss of the transmission data.Accordingly, a recalculation of the path metric is executed (stepS1406). For example, a recalculation of the path metric is executed, byhaving the wireless communication apparatus 100 transmit a path request(PREQ) at the time when operating as a transmission source of multi-hoptransmission, or transmit a path error (PERR) at the time when operatingas a relay station. By changing the transmission power, and afterwardsperforming a recalculation of the metric by the transmission of a PREQor PERR, it becomes possible for a terminal station to select a pathcorresponding to the transmission power at an early stage (same asabove). However, it will be arbitrary whether or not a recalculation ofthe path metric is also performed, along with a change of thetransmission power.

Further, FIG. 15 shows another process procedure, in the form of a flowchart, for the wireless communication apparatus 100 to control thetransmission power in accordance with the stability degree of a path.

First, the influence degree estimation unit 124 measures at least onefrom among a path metric, the number of links, and a traffic amount onlyfor a fixed time, and retains a variation amount of a past fixed time,as a value which shows the stability degree of a path (step S1501).

Next, in order for a change of the transmission power, first, a minimumtransmission power is calculated (step S1502). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data.

Then, when the transmission power is determined, based on a relationshipbetween the variation amount obtained in step S1501 and the minimumtransmission power obtained in step S1502 (step S1503), the transmissionpower determination unit 114 outputs an instruction of poweramplification to the RF transmission unit 113, so as to change to thistransmission power (step S1504). Note that, the changed transmissionpower is used for all of the transmission packets including a beacon.

Next, the signal detection capability control unit 125 performs anadjustment so as to not detect a packet received with a low power, bychanging the signal detection capability in the demodulation unit 122within the reception unit 120 (step S1505) (same as above). However, itwill be arbitrary whether or not an adjustment of the signal detectioncapability is also performed, along with a change of the transmissionpower.

Further, since discrepancies in the actual value are produced with thecalculated path metric, and defects occur such as a packet loss of thetransmission data, by the transmission power after being changed, arecalculation of the path metric is executed (step S1506). However, itwill be arbitrary whether or not a recalculation of the path metric isalso performed, along with a change of the transmission power.

Here, a supplemental remark will be described for a method whichdetermines the transmission power based on a relationship between thevariation amount (stability degree of path) and the minimum transmissionpower in step S1503.

For example, a look-up-table which obtains a transmission power from thevariation amount and the minimum transmission power can be created inadvance based on experiments, simulation calculations or the like, thiscan be stored in a Read Only Memory (ROM) or the like, and atransmission power can be obtained, by applying the values calculated insteps S1501 and S1502 to this look-up-table.

Alternatively, an appropriate transmission power can be obtained, bycreating a graph representing a relationship between the transmissionpower and the variation amount (stability degree of path), and applyingthe variation amount (stability degree of path) obtained in step S1501to this graph, such as shown in FIG. 16, based on the values calculatedby steps S1501 and S1502. In the graph shown in FIG. 16, a maximum value1601 of the transmission power is a value, for example, which isdetermined by an output limit of the RF transmission unit 113 within thetransmission unit 110. Further, a minimum value 1602 of the transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained, and iscalculated in step S1502. Further, a lower threshold 1 and an upperthreshold 2 of the variation amount shown by reference numerals 1603 and1604 are determined by a request or the like of an application whichrequests data transfer. In this way, when the variation amount 1506obtained in step S1501 is applied to the obtained graph 1605, atransmission power 1607 is determined.

Note that, in the case where new traffic has been generated, such as anew application starting up by the upper layer processing unit 130, thewireless communication apparatus 100 reconsiders the setting of thetransmission power, at a regular timing. In this case, the transmissionpower may return up until a maximum value, and a minimal transmissionpower may be recalculated. Reconsideration of the setting of thetransmission power, in accordance with the start of a new applicationand at a regular timing, corresponds not only to the third embodiment,but also to the first embodiment and the second embodiment.

By performing a control of the transmission power in accordance with thestability degree of a path such as shown in FIG. 14 and FIG. 15, thewireless communication apparatus 100 can improve a transmissionopportunity of other terminal stations, in the case where a terminalstation which becomes a communication partner is fixed, and data to betransmitted and received does not vary.

(2) Transmission Power Control for Limiting the Addition of New Links

-   There is a difficult condition in which a terminal station which is    busy with data transmission and reception of itself and has no room    to accept new traffic, or a terminal station which has no room for    power in order to operate by batteries, provides a release for other    terminal stations. However, in a wireless mesh network, a path    metric is calculated and a relay node is set based on this result.    In other words, since a condition such as that described above    within a relay node is not considered in the selection of a path,    the possibility of providing an undesirable link is produced, such    as including a terminal station in a relay node which has no room    for a resource.

Accordingly, the influence degree estimation unit 124 comprehends thecondition of a terminal station itself as an influence degree given toitself by data transmission and reception of itself, and thetransmission power control unit 114 performs a control of thetransmission power in accordance with the condition of the terminalstation itself.

For example, in the case where there is a condition in which it may benecessary for a terminal station to avoid the occurrence of new links,data transfer is performed by a minimal transmission power at which thepresent traffic is able to be provided. When the terminal stationchanges the transmission power, a recalculation of a path metric isexecuted. As a result of this, there will be a low possibility of aterminal station set to a minimal transmission power being used as arelay node of another link.

Further, at the time when a limit of new links becomes unnecessary, suchhaving the present traffic of itself ended, or connecting to an AC powersupply, a terminal station has new links accepted (as a relay node), byreturning the transmission power to the original state.

FIG. 17 shows a process procedure, in the form of a flow chart, for thewireless communication apparatus 100 to control the transmission powerin accordance with the condition of itself.

First, the influence degree estimation unit 124 comprehends thecondition of the wireless communication apparatus 100 itself (stepS1701). In order to comprehend the condition of the wirelesscommunication apparatus 100 itself, the influence degree estimation unit124 may cooperate, for example, with the upper layer processing unit130, or a function module other than this (not illustrated in FIG. 1).

Then, the influence degree estimation unit 124 checks whether or not theaddition of new links is to be limited, based on the comprehendedcondition (step S1702). For example, in the case where it is busy withdata transmission and reception of itself and there is no room to acceptnew traffic, or there is no room for power in order to operate bybatteries, it is decided that the addition of new links is to be limited(Yes in step S1702). In this case, an instruction is output from theinfluence degree estimation unit 124 to the transmission power controlunit 114, so as to perform a change of the transmission power whichperforms data transmission from the transmission unit 110.

In order for a change of the transmission power, first, a minimumtransmission power is calculated (step S1703). A minimum transmissionpower is a transmission power which becomes a necessary minimum limit atwhich the present data transfer is able to be retained. A minimumtransmission power is calculated, for example, in the influence degreeestimation unit 123 or the upper layer processing unit 130, based on adata transfer speed necessary for presently transferred data, path lossinformation obtained from an RSSI or MCS, and a QoS of data.

Then, the transmission power control unit 114 outputs an instruction ofpower amplification to the RF transmission unit 113, so as to change tothe minimum transmission power (step S1704). Note that, the calculatedtransmission power is used for all of the transmission packets includinga beacon.

A terminal station can limit the addition of new links, by causing thetransmission power to be reduced, and can be devoted to datatransmission and reception of itself, or can secure a battery operationtime.

On the other hand, at the time where it may not be necessary to limitthe addition of new links, by having a limit of new links becomeunnecessary or the like, such as having the present traffic of itselfended, or connecting to an AC power supply (No in step S1702), theinfluence degree estimation unit 124 performs an instruction to thetransmission power control unit 114 so as to return, to the originalstate, the transmission power reduced to the minimum transmission power(step S1707). In this way, this wireless communication apparatus 100 hasnew links accepted which become a relay node. Further, a margin of thetransmission power for surely performing data transmission can besecured.

At the time when the transmission power is changed in step S1704 or stepS1707, in combination with this, the signal detection capability controlunit 125 performs an adjustment so as to not detect a packet receivedwith a low power, by changing the signal detection capability in thedemodulation unit 122 within the reception unit 120 (step S1705) (sameas above). However, it will be arbitrary whether or not an adjustment ofthe signal detection capability is also performed, along with a changeof the transmission power.

Further, at the time when the transmission power is changed in stepS1704 or step S1707, there will be the possibility that discrepancies inthe actual value are produced with the calculated path metric, anddefects occur such as a packet loss of the transmission data.Accordingly, a recalculation of the path metric is executed (stepS1706). For example, a recalculation of the path metric is executed, byhaving the wireless communication apparatus 100 transmit a path request(PREQ) at the time when operating as a transmission source of multi-hoptransmission, or transmit a path error (PERR) at the time when operatingas a relay station. By changing the transmission power, and afterwardsperforming a recalculation of the metric by the transmission of a PREQor PERR, it becomes possible for a terminal station to select a pathcorresponding to the transmission power at an early stage (same asabove). However, it will be arbitrary whether or not a recalculation ofthe path metric is also performed, along with a change of thetransmission power.

(3) Transmission Power Control in the Case where there is Room for aLink Condition of a Peer

-   Up until here, embodiments have been described in which a control of    the transmission power is performed, by taking into consideration an    influence degree which a terminal station gives to other terminal    stations by data transmission and reception of itself, and a request    according the condition of itself.

However, in the case where there is no influence degree to otherterminal stations or no request of itself, by positively controlling thetransmission power, it will be useful for an improvement of atransmission opportunity of other terminal stations. Such a positivetransmission power control can be performed in the case where a terminalstation has room for a link condition of a peer.

FIG. 18 shows a process procedure, in the form of a flow chart, for thewireless communication apparatus 100 to positively control thetransmission power.

First, the influence degree estimation unit 124 estimates a linkcondition of a peer of the wireless communication apparatus 100 itself(step S1801). The influence degree estimation unit 124 estimates a linkcondition of a peer with this terminal station, for example, based on anMCS used for transmission to a certain terminal station, a receptionRSSI from this terminal station, and a report value of an RSSI from thisterminal station. In order to comprehend a link condition of a peer, theinfluence degree estimation unit 124 may cooperate, for example, withthe upper layer processing unit 130, or a function module other thanthis (not illustrated in FIG. 1).

Then, the influence degree estimation unit 124 checks whether or not theaddition of new links is to be limited, based on the comprehendedcondition (step S1802).

For example, in the case where an MCS (or a Phy rate) used fortransmission to this terminal station is sufficiently high, and there isstill room for a reception RSSI from this terminal station and a reportvalue of an RSSI from this terminal station, it is decided that there isroom for a link condition of this peer (Yes in step S1802). In thiscase, an instruction is output from the influence degree estimation unit124 to the transmission power control unit 114, so as to perform achange of the transmission power which performs data transmission fromthe transmission unit 110.

In order for a change of the transmission power, first, a minimumtransmission power to transmit a packet to this terminal station iscalculated (step S1803). A minimum transmission power is a transmissionpower which becomes a necessary minimum limit at which the present datatransfer is able to be retained. A minimum transmission power iscalculated, for example, in the influence degree estimation unit 123 orthe upper layer processing unit 130, based on a data transfer speednecessary for presently transferred data, path loss information obtainedfrom an RSSI or MCS, and a QoS of data.

Then, the transmission power control unit 114 outputs an instruction ofpower amplification to the RF transmission unit 113, so as to change thetransmission power of a transmission packet to this terminal station tothe minimum transmission power (step S1804). By causing the transmissionpower used for a link of a peer to be reduced, it will be useful for animprovement of a transmission opportunity of other terminal stations.

On the other hand, in the case where there is no room for a linkcondition of a peer (No in step S1802), the influence degree estimationunit 124 performs an instruction to the transmission power control unit114 so as to return, to the original state, the transmission powerreduced to the minimum transmission power (step S1807). In this way, alink of a peer is maintained.

At the time when the transmission power is changed in step S1804 or stepS1807, in combination with this, the signal detection capability controlunit 125 performs an adjustment so as to not detect a packet receivedwith a low power, by changing the signal detection capability in thedemodulation unit 122 within the reception unit 120 (step S1805) (sameas above). However, it will be arbitrary whether or not an adjustment ofthe signal detection capability is also performed, along with a changeof the transmission power.

Further, at the time when the transmission power is changed in stepS1804 or step S1807, there will be the possibility that discrepancies inthe actual value are produced with the calculated path metric, anddefects occur such as a packet loss of the transmission data.Accordingly, a recalculation of the path metric is executed (stepS1806). For example, a recalculation of the path metric is executed, byhaving the wireless communication apparatus 100 transmit a path request(PREQ) at the time when operating as a transmission source of multi-hoptransmission, or transmit a path error (PERR) at the time when operatingas a relay station. By changing the transmission power, and afterwardsperforming a recalculation of the metric by the transmission of a PREQor PERR, it becomes possible for a terminal station to select a pathcorresponding to the transmission power at an early stage (same asabove). However, it will be arbitrary whether or not a recalculation ofthe path metric is also performed, along with a change of thetransmission power.

According to the third embodiment, by controlling the transmission powerbased on the condition of itself, such as the form of the power supply,the transmission and reception partner, or the time, it becomes possiblefor the wireless communication apparatus 100 to perform a setting of asmooth path in a mesh network, such as changing the path metric oravoiding an unnecessary relay.

Further, according to the third embodiment, by using a minimaltransmission power corresponding to the service of data to betransferred or a QoS, a terminal station can suppress interference toother terminal stations, and can prevent a reduction of a transmissionopportunity of other terminal stations.

Further, according to the third embodiment, by performing a change of asignal detection capability together with a change in a transmissionpower of itself, a terminal station can reduce the non-uniformity of atransmission opportunity between terminal stations.

Further, according to the third embodiment, by changing a transmissionpower or a signal detection capability of itself, and afterwardsperforming a recalculation of a path metric by the transmission of aPREQ or PERR, it becomes possible for a terminal station to perform aselection of a path corresponding to the transmission power at an earlystage.

Embodiment 4

-   In order for a terminal station to determine a transmission    parameter such as an MCS, information of a path loss may be    necessary. In the case where there is no transmission power control,    that is, in the case where the transmission power of all terminal    stations is fixed, a reception RSSI can be measured from a certain    terminal station, and a path loss can be estimated by taking a    difference with the transmission powers. However, in the above    described first through to third embodiments, since a terminal    station performs a control of the transmission power, the    transmission power of other terminal stations is unclear, and a path    loss is not able to be estimated. Accordingly, the above described    problem (4) is brought about.

Accordingly, hereinafter, a method will be described in which a numberof transmission powers of other terminals are acquired.

(1) Method in which transmission power information is added to anexisting frame and transmitted

-   A beacon frame can be included as an existing frame to which    transmission power information is added. In a wireless LAN standard    such as IEEE802.11, in order to transfer whether or not    communication is possible, a communication station prescribes that a    beacon frame is to be broadcast in a fixed time interval. Various    information elements (Information Element: IE) can be stored in a    frame body of a beacon frame. A Vendor Specific IE is defined as one    of these. A Vendor Specific IE is an information element capable of    being freely added and used by a vendor. In the present embodiment,    by storing information of the transmission power in this information    element within a beacon frame, and mutually using it, each of the    terminal stations can mutually acquire the transmission power.

Further, a notification frame of the transmission power can be includedas an existing frame to which transmission power information is added.In IEEE802.11, a mechanism which notifies the transmission power isprepared, with the aim of suppressing interference to other systemsmainly using 5 GHz. According to this mechanism, a frame Transmit PowerControl (TPC) Request, in which one of the terminal stations requests anotification of the transmission power to another terminal station, anda frame TPV Report, in which the other terminal station receiving thisrequest notifies the transmission power, are defined. This mechanism canbe used by any band. In the present embodiment, a notification of thetransmission power can be performed by using these frames. It isneedless to say that transmission power information may be broadcast,multicast, or unicast, as a data packet of an IP layer, without using anexisting frame.

As described above, according to a method in which transmission powerinformation is added to an existing frame and transmitted, by addingtransmission power information to a Vendor Specific IE of a beacon frameor an Action frame related to transmission power control, a terminalstation can notify information of the present transmission power to acommunication partner. Therefore, by estimating a path loss based onreceived information of the transmission power and a reception RSSI, atthe terminal station side of a communication partner, a more accurateMCS can be determined.

(2) Method in which the transmission power is estimated, without anotification of the transmission power

-   It is possible for terminal stations periodically performing data    transfer to estimate the transmission power, even if not notifying    information of the transmission power. This uses an MCS used by a    terminal station of a communication partner.

A transmission MCS is generally calculated and determined based on apath loss and a packet error rate. Therefore, by measuring an MCS usedfor a data packet transmitted from a terminal station of a communicationpartner, and a packet error rate of a packet transmitted from thisterminal station, a path loss can be back calculated. Also, since areception RSSI can be measured, the terminal station can estimate thetransmission power of a communication partner, based on the backcalculated path loss and the RSSI.

FIG. 19 shows a process procedure, in the form of a flow chart, forestimating the transmission power without a notification of thetransmission power. While the following process can be performed by theupper layer processing unit 130, for example, it may also be performedby another function module.

First, an MCS used for a data packet transmitted from a terminal stationof a communication partner is figured out, by decrypting thetransmission data after being decoded by the channel decoding unit 123(step S1901).

Further, a packet error rate of a packet transmitted from this terminalstation is measured (step S1902).

Next, a path loss is back calculated, from the MCS of the communicationpartner and the measured packet error rate (step S1903).

Further, an RSSI of a reception packet is measured, in parallel with theabove description (step S1904).

Then, the transmission power of the communication partner is estimated,based on the path loss back calculated in step S1903, and the RSSImeasured in step S1904 (step S1905).

-   In this way, each of the terminal stations can estimate the    transmission power without a notification from a communication    partner, and can determine a more accurate MCS, based on an MCS and    a reception RSSI used by the communication partner.

CITATION LIST Patent Literature 1:

JP 2005-253047A

-   Patent Literature 2:

JP 2005-33557A

INDUSTRIAL APPLICABILITY

So far, the embodiment of the present disclosure has been described indetail with reference to a specific embodiment. However, it should benoted that various variations and alternative embodiments will becomeapparent to those skilled in the art without departing from the scope ofthe present disclosure.

While a description has been made in the present disclosure whichcenters on embodiments applied to a wireless network in which eachterminal station performs autonomous distribution, such as an Ad-hocnetwork or a mesh network, the technology disclosed in the presentdisclosure is not limited to this. The technology disclosed in thepresent disclosure can be applied to various types of wireless networks,in which access to a media is controlled in accordance with an occupancystate of the media starting CSMA by each terminal station, and cansuppress useless interference between terminal stations, and improve atransmission opportunity of each terminal station.

In short, the present technology has been disclosed in a form ofillustration and should not be interpreted limitedly. To determine thegist of the present disclosure, patent claims should be taken intoaccount.

Additionally, the Present Technology may also be Configured as Below.

(1)

A wireless communication apparatus including:

a transmission unit which transmits a wireless signal;

a reception unit which receives a wireless signal;

an influence degree estimation unit which estimates an influence degreegiven to a surrounding terminal station by transmission data from thetransmission unit; and

a transmission power control unit which controls a transmission power ofthe transmission unit based on the influence degree.

(2)

The wireless communication apparatus according to (1),

wherein the transmission power control unit controls a transmissionpower of the transmission unit based on the influence degree and aminimum transmission power capable of retaining a present data transfer.

(3)

The wireless communication apparatus according to (2),

wherein a minimum transmission power capable of retaining a present datatransfer is calculated based on a data transfer speed necessary forpresently transferred data, path loss information obtained from an RSSIor MCS, and a QoS of data.

(4)

The wireless communication apparatus according to (2),

wherein, at a time when the influence degree exceeds a prescribed value,the transmission power control unit changes a transmission power of thetransmission unit to the minimum transmission power.

(5)

The wireless communication apparatus according to (2),

wherein the transmission power control unit changes a transmission powerto a transmission power corresponding to a relationship between theinfluence degree and the minimum transmission power.

(6)

The wireless communication apparatus according to (1),

wherein a signal detection capability in the reception unit iscontrolled in accordance with a change in a transmission power of thetransmission unit.

(7)

The wireless communication apparatus according to (1),

wherein the wireless communication apparatus performs a communicationoperation by a mesh network, and

wherein a metric of a path is recalculated in accordance with a changein a transmission power of the transmission unit.

(8)

The wireless communication apparatus according to (1),

wherein the influence degree estimation unit measures a traffic amountto be handled by the transmission unit and the reception unit as theinfluence degree.

(9)

The wireless communication apparatus according to (8),

wherein the influence degree estimation unit measures a traffic amountby counting the number of packets or a size of packet to be transmittedand received by the transmission unit and the reception unit.

(10)

The wireless communication apparatus according to (1),

wherein the influence degree estimation unit measures the number oflinks as the influence degree.

(11)

The wireless communication apparatus according to (1),

wherein the influence degree estimation unit additionally estimates aninfluence degree given to the wireless communication apparatus itself bytransmission data from the transmission unit, and

wherein the transmission power control unit controls a transmissionpower of the transmission unit based on the influence degree.

(12)

The wireless communication apparatus according to (11),

wherein the influence degree estimation unit estimates a stabilitydegree of a path of the wireless communication apparatus, and

wherein the transmission power control unit controls a transmissionpower of the transmission unit based on the stability degree of thepath.

(13)

The wireless communication apparatus according to (12),

wherein the influence degree estimation unit estimates the stabilitydegree of the path based on a variation amount of a path metric, thenumber of links, and a traffic amount, in at least one fixed time in thepast.

(14)

The wireless communication apparatus according to (11),

wherein the influence degree estimation unit estimates whether or notthere is a condition where an addition of a new link is to be limited bythe wireless communication apparatus, and

wherein the transmission power control unit controls a transmissionpower in accordance with the condition.

(15)

The wireless communication apparatus according to (14),

wherein the influence degree estimation unit estimates whether or notthere is a condition where an addition of a new link is to be limitedbased on at least one of a present traffic and power supply state.

(16)

The wireless communication apparatus according to (11),

wherein the influence degree estimation unit estimates a link conditionof a peer with a certain terminal station, and

wherein the transmission power control unit controls a transmissionpower in accordance with the link condition.

(17)

The wireless communication apparatus according to (16), wherein theinfluence degree estimation unit estimates the link condition based onat least one of an MCS used for transmission to the terminal station, areception RSSI from the terminal station, and a report value of an RSSIfrom the terminal station.

(18)

The wireless communication apparatus according to (1),

wherein another terminal station is notified of information of atransmission power changed by the transmission power control unit.

(18-1)

The wireless communication apparatus according to (18),

wherein information of the transmission power is stored in a VendorSpecific IE within a beacon frame and notified.

(18-2)

The wireless communication apparatus according to (18),

wherein information of the transmission power is notified to anotherterminal station as a TPC Report which responds to a notificationrequest TPC Request of a transmission power from the another terminalstation.

(19)

The wireless communication apparatus according to (1),

wherein a path loss is back calculated from an MCS used for a datapacket transmitted from a terminal station of a communication partner,and a packet error rate of a packet transmitted from the terminalstation, and a transmission power of the communication partner isestimated based on the path loss and a reception RSSI.

(20)

A wireless communication method including:

an influence degree estimation step which estimates an influence degreegiven to a surrounding terminal station by transmission data; and

a transmission power control step which controls a transmission power ata time of data transmission based on the influence degree.

REFERENCE SIGNS LIST

-   100 wireless communication apparatus-   101 antenna-   110 transmission unit-   111 channel encoding unit-   112 modulation unit-   113 RF transmission unit-   114 transmission power control unit-   120 reception unit-   121 RF reception unit-   122 demodulation unit-   123 channel decoding unit-   124 influence degree estimation unit-   125 signal detection capability control unit-   130 upper layer processing unit

1. A wireless communication apparatus comprising: a transmission unitwhich transmits a wireless signal; a reception unit which receives awireless signal; an influence degree estimation unit which estimates aninfluence degree given to a surrounding terminal station by transmissiondata from the transmission unit; and a transmission power control unitwhich controls a transmission power of the transmission unit based onthe influence degree.